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OLD THREAD DAC End by Andrea Ciuffoli

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H/V Test with 30ma load

H/V fine.
From left AC input, V(R3), V(C9)(C8).
AC Input 261V
V(R3)=336VDC
V(C9)(C8)=269.3VDC
Load current=30mA
R1=22K, R2=100K
67V headroom for the regulator.
Run up time ~60min
Heatsink on IRF840 7.5C/W
IRF840 Temperature=46C
Room Temperature=27C
 

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Which particular ones? It looks correct to me? However i'm a noob :p


Edit: C11 ;). I got ya.

Yep, it's C11 for sure.
Notice on this pic, the trace is on the other side, to what is shown on the board.
http://www.audiodesignguide.com/DACend2/Picture-077.jpg

Is this what you mean....

An externally hosted image should be here but it was not working when we last tested it.


So we just have to change the switch + sign to - right....!!!!

Anymore mistakes need to highlight here ?????
 
Is this what you mean....

An externally hosted image should be here but it was not working when we last tested it.


So we just have to change the switch + sign to - right....!!!!

Anymore mistakes need to highlight here ?????

No, only C11 needs to be rotated, then the board PASS. I mean this HV PSU board.
The other three need to be checked.
 
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It looks like that the number 11 brings bad luck on H/V PSU board.

I can find 200R trimmer for the heater section. It seems that 220R is not popular.
With 200R trimmer and 9VAC input measured, output voltage cannot be adjusted below 7VDC then the heater bye bye.
I replaced R11 with 560R and you can obtain 6.3V near centre trimmer.

Heater DC output loaded with 1.38A
AC input 9.4V measured
Output 6.3VDC
Temperatures:
LM338 61C
R8 and R9 140C (mounted as Goalpost)
Bridge rectifier 80C
Transformer 33C


Picture shows PSU fully loaded.
 

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It looks like that the number 11 brings bad luck on H/V PSU board.

I can find 200R trimmer for the heater section. It seems that 220R is not popular.
With 200R trimmer and 9VAC input measured, output voltage cannot be adjusted below 7VDC then the heater bye bye.
I replaced R11 with 470R and you can obtain 6.3V near centre trimmer.

Heater DC output loaded with 1.38A
AC input 9.4V measured
Output 6.3VDC
Temperatures:
LM338 61C
R8 and R9 140C (mounted as Goalpost)
Bridge rectifier 80C

Picture shows PSU fully loaded.

hot! they are droping about 1.5v (ish) the reg has a pretty good sink on it, maybe better to let the reg burn off the heat. dont know without playing
 
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hot! they are droping about 1.5v (ish) the reg has a pretty good sink on it, maybe better to let the reg burn off the heat. dont know without playing

You are right. 1.5V drop
The resistors are wirewound 4 watt and the current dissipation is 1W each.
The resistors are ok at that temperature but I want to avoid long term dry solder joints. The resistors are clear from the PCB about 5mm. Any suggestion?
I guess that's the way it is. The only thing to do is to reduce the resistor's value.
 
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You are using the LM338 reg correct?
If the 317 was used (as labeled on the board) do you think this will make any substantial difference to the output voltage, still using 1k and a 200r trim?
Or even the LT1084 as described in the BOM. Also would this help drop the temperature of R8 and R9?

Sorry for the noob questions/ suggestions. :eek:
 
Cool, you're right. Thanks a lot to apelizzo, yes. I had just soldered my caps in yesterday (the wrong way around) so in maybe a weeks time there would have been a bang :p. Saved now :).

I'll throughly look over the boards again, see if i can spot any other errors.
Will changing the 1k resistor to a 560r modify anything else other than the range available for the trimmer?
It's just a little strange the way the silk screen has 200r on the trimmer, yet both the BOM's say 220r.
 
You are using the LM338 reg correct?
If the 317 was used (as labeled on the board) do you think this will make any substantial difference to the output voltage, still using 1k and a 200r trim?
Or even the LT1084 as described in the BOM. Also would this help drop the temperature of R8 and R9?

Sorry for the noob questions/ suggestions. :eek:

The LM338 replaced the LM317 because the LM317 (unless is LM317K) is rated only 1.5A so it was pulled to the limit.
As you see in my test for the LM338 I needed to run at least 9VAC input because the high dropout voltage of the LM338 . If you use LT1085 you may use slightly lower voltage. Or the other way around, if your AC voltage on full load is not at least 9V you must replace the LM338 with LT1085.
I had to replace R11 in my case. If I had 220R instead of 200 maybe was just enough to adjust to 6.3V. Not enough play anyway.

With regards to the bang, well.. it would happen after seconds, +/ 1 min. An inverted cap starts gassing and becomes hot very quickly.
 
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No, only C11 needs to be rotated, then the board PASS. I mean this HV PSU board.
The other three need to be checked.

yes This PCb has a bug in the wrong.
You noticed I have marked a square hole or reject the + , alcohol is a circle hole welding -. What is difficult to mistake!
Thank you very much!
Thank apelizzo
 
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I've noticed a few change sin the BOM in the last week, especially for the power supply for the I/V.
Is it better to use this amended list now?
Have the changes been made been tested, also will it fix the voltage and temperature issues?

Also confirm that all diode's in the I/V PS are 1n4007 and 1n5062 has no place there.
What difference will there be also from 1n5062 to the 1n5819, in the salas shunt?
 
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